This description comes from Wikipedia

In The Legend of Zelda: Ocarina of Time, Zelda disguises herself as a surviving male member of the Sheikah clan under the name of Sheik (¥·©`¥¯ Sh¨©ku?). With voice muffled and face concealed, as well as wearing a form-fitting blue unitard with the red Sheikah eye in the center, Sheik is unrecognizable as Zelda.[15] Sheik plays the lyre and teaches Link new songs to help him on his quest. When Link arrives at the Temple of Time near the end of the game, he uses the Triforce of Wisdom and reverts to Zelda. It is claimed by the character's trophy in Super Smash Bros. Melee that Zelda uses her magical skills to change her skin tone, hair length, eye color, and clothing. In the non-canon licensed manga for Ocarina of Time, Zelda instead requests that Impa seal her consciousness away, so that she may become Sheik.[16]

Sheik appears in Super Smash Bros. Melee and Super Smash Bros. Brawl, in which Zelda can change into Sheik as one of her abilities. Sheik's new design in Brawl is based on a model created for consideration in Twilight Princess.[13] Sheik will return in the fourth Super Smash Bros. game, in which she will be a separate character from Zelda.[17]